Abstract
Various derivativei of L-cpteine obtained by conversion to an-S-S-bond in the mucoprotein by means of-SH in the chemical structure are widely used as expectorants because they show mucous dissolving action. Recently, there have been reports that L-cysteine derivatives lower the potencies Of viiious antibiotics.1-5);
Various typet of antibiotiat eyiteine-type expectorants are often used concomitantly for the treatment of bacterial infecticiiis in rispiratory tract diseases, and any decrease in the antibiotic potency presehtt Major t4erapeutic problem.
We invesiigited effects of tour cysteine derivatives on 12 antibiotics, ampicillin (ABPC), amoxicillin (AMPC),(SBPt), cefazolin (CEZ), cephalexin (CEX), cephalothin (CET), oxytetracycline (OTC), doxycycline (DOTC), minocycline (MINO), erythromycin (EM), ribostamycin (YSM) and lincomycin (LCM), widely used clinically in vitro, with the minimum inhibitory concentration (MC) obtained by the liquid dilution method as an index. L-Cysteine, acetylcysteine, ethylcysteine and mecysteine lowered the potencies of almost all of the antibiotics at high concentrations (500mcg/ml), but at low concentrations (12.5mcg/ml), mecysteine lowered the potencies of only three antibiotics and L-cysteine thote of only four antibiotics, while acetylcysteine decreased the potencies of six and ethylcysteine those of seven antibiotics.
